Still, most people don't feel they spend too much time on their phones — only about 39 percent. But one age group among all others is more likely to admit to smart phone overuse: Millennials. Among 18- to 34-year-olds, 60 percent believe they use their phones too much.

About 63 percent of all respondents reported trying to limit their smartphone usage, with roughly half succeeding in cutting back.

Smartphone usage is also blurring the lines between work and leisure: 70 percent of respondents say they use their personal smartphones at least occasionally for work after hours. And more than a third of adults say they use their smartphones "very often" for business purposes outside of normal working hours.